Cerebral hemispheres
thumb|right|200px|The [[human brain as viewed from above, showing the cerebral hemispheres. The anterior aspect (front) of the brain is to the right.]] A cerebral hemisphere (hemispherium cerebrale) is defined as one of the two regions of the brain that are delineated by the body's, the left hemisphere and right hemisphere. median plane. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is supported by an inner layer of white matter. The hemispheres are linked by the corpus callosum, a very large bundle of nerve fibers, and also by other smaller commissures, including the anterior commissure, posterior commissure, and hippocampal commissure. These commissures transfer information between the two hemispheres to coordinate localized functions. The architecture, types of cells, types of neurotransmitters and receptor subtypes are all distributed among the two hemispheres in a markedly asymmetric fashion. However, it must be noted that, while some of these hemispheric distribution differences are consistent across human beings, or even across some species, many observable distribution differences vary from individual to individual within a given species. Lobes thumb|right|200px|Lobes of the human brain viewed from the right side. The frontal lobe is demarcated in red, the parietal lobe in orange, the occipital lobe in yellow, and the temporal lobe in green. Neurologists subdivide the cerebral cortex into the following four lobes: * the frontal lobe - the most anterior (rostral) portion of the brain, toward the face * the parietal lobe - immediately posterior to (behind) the frontal lobe * the occipital lobe - the farthest posterior region, nearest the spine * the temporal lobe - underneath (inferior to) the other cortices, the temporal lobe in humans sits near the "temples" of the face Neurologists also recognize two additional areas of the cerebral cortex: * the limbic system - including the cingulate cortex, located above the corpus callosum * the insular cortex - buried within the lateral sulcus. The hemispheres are linked by the corpus callosum, a very large bundle of nerve fibers, and also by other smaller commissures, including the anterior commissure, posterior commissure, and hippocampal commissure. These commissures transfer information between the two hemispheres to coordinate localized functions. Embryological development The cerebral hemispheres are derived from the telencephalon. They arise five weeks after conception as bilateral invaginations of the walls. The hemispheres grow round in a C-shape and then back again, pulling all structures internal to the hemispheres (such as the ventricles) with them. The interventricular foramen (sometimes called the interventricular foramena of munro) allows communication with the lateral ventricle. The choroid plexus is formed from ependymal cells and vascular mesenchyme. Hemisphere lateralization Broad generalizations are often made in popular psychology about certain function (eg. logic, creativity) being lateralised, that is, located in the right or left side of the brain. These ideas need to be treated carefully because the popular lateralizations are often distributed across both sides.Western et al. 2006 "Psychology: Austraian and New Zealand edition" John Wiley p.107 However, there is some division of mental processing. Researchers have been investigating to what extent areas of the brain are specialized for certain functions. If a specific region of the brain is injured or destroyed, their functions can sometimes be recovered by neighboring brain regions — even opposite hemispheres. This depends more on the age and the damage occurred than anything else. The best evidence of lateralization for one specific ability is language. Both of the major areas involved in language skills, Broca's area and Wernicke's area, are in the left hemisphere. Perceptual information from the eyes, ears, and rest of the body is sent to the opposite hemisphere, and motor information sent out to the body also comes from the opposite hemisphere (see also primary sensory areas). Neuropsychologists (e.g. Roger Sperry, Michael Gazzaniga) have studied split-brain patients to better understand lateralization. Sperry pioneered the use of lateralized tachistoscopes to present visual information to one hemisphere or the other. Scientists have also studied people born without a corpus callosum to determine specialization of brain hemispheres. The magnocellular pathway of the visual system sends more information to the right hemisphere, while the parvocellular pathway sends more information to the left hemisphere. There are higher levels of the neurotransmitter norepinephrine on the right and higher levels of dopamine on the left. There is more white-matter (longer axons) on right and more grey-matter (cell bodies) on the left.R. Carter, Mapping the Mind, Phoenix, London, 2004, Originally Weidenfeld and Nicolson, 1998. Linear reasoning functions of language such as grammar and word production are often lateralized to the left hemisphere of the brain. In contrast, holistic reasoning functions of language such as intonation and emphasis are often lateralized to the right hemisphere of the brain. Other integrative functions such as intuitive or heuristic arithmetic, binaural sound localization, emotions, etc. seem to be more bilaterally controlled.Dehaene S, Spelke E, Pinel P, Stanescu R, Tsivkin S. Sources of mathematical thinking: behavioral and brain-imaging evidence. Science. 1999 May 7;284(5416):970-4. PMID 10320379. except the mathematics and time claims, which are both unreferenced, all from Taylor, Insep and Taylor, M. Martin (1990) "Psycholinguistics: Learning and using Language". page 367 References * The Emerging Mind; Vilayanur S. Ramachandran; Reith Lectures 2003. * More information on these lobes can be found in a book by Dr. Eric Braverman "The Edge Effect." Reference * The Emerging Mind; Vilayanur S. Ramachandran; Reith Lectures 2003. * R. Carter, Mapping the Mind, Phoenix, London, 2004, Originally Weidenfeld and Nicolson, 1998. * More information on these lobes can be found in a book by Dr. Eric Braverman "The Edge Effect." See also * Roger Wolcott Sperry * Michael Gazzaniga * Paul Pierre Broca * Manas K Mandal * Hemispherectomy External links * Test your sidedness * A recent article Category:Cerebrum